Direct tests of haplodiploid inheritance in Thrips tabaci (Thysanoptera: Thripidae) using parent-offspring SSR-GBS

Haplodiploidy is a sex determination system in which males are haploid and females are diploid. In the typical haplodiploid system, females inherit half of their genome from each parent, whereas males inherit a haploid genome exclusively from their mother. However, several exceptions to this pattern have recently been reported in some insects and spider mites, underscoring the need for rigorous genetic analyses of inheritance patterns in other haplodiploid species. Thrips (order Thysanoptera) are a major clade that exhibits haplodiploidy. Here, we investigated inheritance in the onion thrips, Thrips tabaci, by comparing parent-offspring genotypes using an amplicon-based microsatellite genotyping-by-sequencing method (Short Sequence Repeats-Genotyping by Sequencing, SSR-GBS). We successfully genotyped eight loci across eight families from the sexual lineage and additionally analyzed five families from the thelytokous lineage, including both diploid and triploid strains. In the sexual lineage, segregation conformed to arrhenotoky: F1 females inherited one allele from each parent, and F1 males carried a single maternal allele. In the thelytokous lineage, offspring inherited only alleles present in the mother. Compared with fragment-length genotyping, SSR-GBS increased the mean number of alleles detected per locus by 28% and reduced the rate of size homoplasy (alleles of the same size but different sequences), yielding clearer separation of the sexual and thelytokous lineages. These findings advance our understanding of the evolution of reproductive systems in this major haplodiploid clade and demonstrate the utility of SSR-GBS for high-resolution SSR genotyping.